The proper maintenance of contact lenses requires periodic sterilization or disinfection to eliminate harmful bacteria and other microorganisms. A number of maintenance processes involve chemical reactions which involve the generation of gaseous by-products. For example, one conventional method of disinfecting contact lenses involves contacting them with a dilute solution of hydrogen peroxide. See, for example, U.S. Pat. No. 3,912,451 to Gaglia. By immersing a contact lens in a solution of hydrogen peroxide in a container, sterilization of the lens is relatively quickly accomplished.
Although hydrogen peroxide is highly effective in disinfecting contact lenses, hydrogen peroxide must be removed from solution in contact with the lenses prior to placing the lenses in a patient's eye, since the peroxides would otherwise cause eye irritation and patient discomfort. Typically, an agent for decomposing or "neutralizing" the peroxide into water and gaseous oxygen is present so that peroxide is reduced to a satisfactory level before the treated lens is removed from the solution in the container. The neutralizing agent typically may be a metal catalyst such as platinum or an enzyme such as catalase.
Because gaseous oxygen is produced by the neutralizing agent following oxidative disinfection it is necessary to avoid the buildup of excessive internal gas pressure in the container holding the lenses in solution. On the other hand, it is desirable that a lens case not allow indiscriminate leakage of liquid so that the peroxide solution does not escape from the container if the container is moved from the vertical or falls on its side. The container is, therefore, typically scaled to prevent liquids from being discharged from the container during the disinfection of the lenses and the neutralization of the disinfectant. A seal between the container and its cap should be designed to prevent spillage of liquid if the container falls on its side or is upset during transport. Typically, this means that when the pressure is near atmospheric pressure, little or no liquid can escape from the container even if held upside down.
In view of the need to both prevent the leakage of the disinfecting solution and to allow the discharge of gas when pressure builds up in the container, containers have been designed to provide a mechanism for the venting gases to the environment while otherwise maintaining a seal that is selectively resistant or impervious to the passage of liquids. Such venting mechanism is necessary in order to avoid risking fracture and/or explosion of the closed container.
A wide variety of venting and sealing means for lens cases have been developed for the above purpose. One approach has been to employ a gas-permeable, liquid-impermeable membrane having a porosity and/or hydrophobicity that allows gas but not liquid to escape from the lens case. For example, U.S. Pat. No. 4,396,583 to LeBoeuf discloses a vented case having a cavity in its cap for supporting a vapor-permeable, liquid impermeable barrier through which gas is vented. Similarly, Ryder et al. in U.S. Pat. No. 4,637,919 describes a contact lens cleaning container having a mating cap in which a filter assembly is positioned in a vent passageway. The filter assembly includes a hydrophobic membrane that continuously vents the gas generated within the container during the decomposition of peroxide. The pores in the hydrophobic membrane are sufficiently small to inhibit liquid leakage from the container while allowing the passage of gas under pressure.
U.S. Pat. No. 5,366,078 to Braun discloses a lens case having cap on the inner surface of which is positioned a hollow pedestal. Inside the hollow pedestal is sealingly positioned a hydrophobic impermeable gasket adjacent to an aperture in the top surface of the cap for discharging gas. The gasket fits snugly into the hollow pedestal and is provided with an aperture of sufficient dimension to discharge gas at an appropriate rate but small enough so that there is no significant discharge of liquid from the system even when the case is inverted or lies horizontally.
Another approach to venting lens cases has been to provide a deflectable gasket or diaphragm that resiliently deflects under pressure to allow the release of gas. For example, U.S. Pat. No. 4,956,156 issued to Kanner et al. discloses a disinfecting system which includes a cap having a bore in which a resiliently-deflectable diaphragm is sealingly positioned to prevent liquid leakage while allowing gas to pass when sufficient internal pressure develops to deflect the diaphragm. In particular, U.S. Pat. No. 4,956,156 discloses the diaphragm deflecting when the pressure exceeds 75 psia. Similarly, U.S. Pat. No. 5,250,266 issued to Kanner discloses a lens treating apparatus, including a container and a cap, in which gas is vented through a type of check valve in the cap. The check valve includes a disc having a linear slit therethrough. The slit generally provides a liquid-impermeable barrier, but when internal pressure is generated, the slit opens to allow gas to pass to the environment. In a slightly different approach, U.S. Pat. No. 4,996,027 issued to Kanner discloses a disinfecting system that comprises a self-reseating unitary gasket positioned between the cap and container of the device to provide a liquid-tight seal. Increased internal pressure during use causes the gasket to unseat at least partially, allowing gas to pass between the cap and container and to the environment.
A known disadvantage of the above venting mechanisms has been their complexity which increases their manufacturing costs. Efforts have been made to reduce the number of separably manufactured parts that need to be assembled in the cap. For example, U.S. Pat. No. 4,750,610 issued to Ryder discloses a disinfecting lens case having a cap that includes a resiliently deflectable flange which acts as a check valve in conjunction with the container rim. In operation, the cap flange is typically in a closed position, thereby preventing liquid leakage. When sufficient internal pressure develops, the cap flange deflects, allowing gas to pass through the loosely threaded container-cap connection to the outside of the container.
Another example of a deflectable venting means is disclosed in U.S. Pat. No. 5,558,846 to Alvord et al. Instead of a flange on the cap deflecting, the periphery of a container is designed to deflect. The cap includes a sealing rim adapted to mate with the periphery of the container at the open end of the container, thereby forming a primary sealing and venting means. When the pressure builds up to a certain point the during neutralization of the peroxide, the plastic at the top of the barrel deforms so as to release pressure. Secondarily, a hole in the cap positioned between the external periphery of the cap and the sealing rim allows gas to escape to the environment. The plastic then returns to the normal configuration when the pressure is below the deformation point. The plastic of the cap remains undeformed or rigid as this is happening. The proper flexing of the container periphery, therefore, depends on reduced strength in the container periphery relative to the cap sealing rim, preferably by reduced thickness relative to the sealing rim.
Alvord et al. state that, both from a manufacturing perspective and from an operational perspective, their device is less complicated than earlier devices that similarly involve resiliently deflectable parts. Since the sealing and venting means is an integrally molded part of the cap and container structure, additional parts are unnecessary.
One disadvantage of the venting mechanism described by Alvord et al. is that it is complicated to design, since the materials used for the container and cap, their properties, and the dimensions of various parts thereof can all affect the relative movement of parts. The materials and dimensions must be selected so that deformation of the container periphery consistently occurs under excessive pressure. Since the flexibility or other properties of the moving parts may change during use, consistency of venting and sealing may be difficult to achieve after extended use. Repeated movements of relatively rigid, highly stressed parts may result in structural fatigue or cracking. Since relatively high pressures are required to deflect the container periphery, there is a greater risk that a failure to vent for some reason, for example if the case fails to deform as expected, might result in the lens case exploding.
The previously described patents describe practical venting alternatives for peroxide-based lens cleaning/disinfecting devices. However, many of the prior systems involve relatively complex structures, increasing the cost of the device, as well as adding to the difficulty of manufacture. Other systems, while having fewer parts and being less costly to manufacture, require complicated engineering design to provide the required movement of certain parts based on material properties and carefully crafted dimensions. It would be desirable to obtain a lens case of simple design which vents gas without requiring extra parts such as membranes, diaphragms or gaskets and without depending on moving parts that must deflect or deform only after relatively high pressure builds up in the lens case. It is would be especially desirable to have a lens case that simply and reliably allows the venting of gaseous by-products without requiring the buildup of high or excessive pressure.